The invention relates to a device for mounting rockbolts.
When permanently safeguarding with rockbolts, e.g. in tunnels, corrosion protection is required. To achieve this, the bolt may be completely moulded by injecting cementing grout or by "cement grouting". The bolts are usually hot galvanized or powder painted.
It is desirable to combine the use of bolts utilized for making a work place safe, without any requirement for corrosion protection, and the succeeding cementing to increase the fastening and establish protection against corrosion.
To achieve this, tube shaped bolts with an expansion bushing at the inner end have been used. This solution to the problem allows later cementing, but is expensive because the cost of tube bolts is approximately twice that of steel bolts. Additionally, this solution is sensitive to incorrect grout consistency.
It has been proposed to after treat steel rods with a cementing hose and a venting tube. A steel rod is fastened at its inner end with an expansion bushing or a plastic grouting, e.g. a polyester cartridge. Additionally a venting tube is introduced to the bottom of the hole and a cementing hose is introduced approximately 25 cm into the hole. The outer part of the hole is then sealed with sealing foam, before introducing of cementing grout. The air in the hole will then expel through the venting tube.
This cementing requires additional mounting time and is impaired by bad sealing with the sealing foam. This results in leakage before the hole is filled and a part of the bolt not being covered by cementing grout.